Rotor blade shrouding



Dec. 6, 1960 H. w. WELSH 2,963,272

ROTOR BLADE SHROUDING Filed July 19, 1957 2 Sheets-sheet 1 Dec. 6, 1960 H. w. WELSH ROTOR BLADE SHROUDING Filed July 19, 1957 2 Sheets-Sheet 2 IN VEN T OR.

ROTOR BLADE SHROUDING Harvey W. Welsh, Indianapolis, Ind., assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed July 19, 1957, Ser. No. 673,055

2 Claims. (Cl. 253-77) My invention relates to shrouded blade structures for the rotors of fluid-dynamic machines such as axial-flow compressors and turbines.

Certain advantages of providing shrouding on the tips of compressor and turbine rotor blades have long been appreciated. The provision of a satisfactory shrouded blade structure involves substantial difficulties, however, particularly in the case of compressor blading of low hub radius to tip radius ratio. In such a case, the blades may be closely spaced at the hub, but are widely spaced at the tip. Since such machines may be of considerable diameter and rotate at high speed, there is a high centrifugal force on the shroud. My invention is directed primarily to the provision of a suitable lightweight shroud structure which will not put a heavy radial load on the blades and yet which is sufficiently rigid that it will not how out to a harmful extent between the blades, and to a simple, lightweight, reliable, and readily applied at tachment for the shroud which makes it practicable to remove the shroud for replacement of damaged blades.

The nature of the invention and the advantages thereof will be apparent to those skilled in the art from the succeeding detailed description of two preferred embodiments of the invention and the accompanying drawings thereof.

Figure 1 is a fragmentary sectional view of the rotor of an axial-flow compressor taken on a plane containing the axis of the rotor.

Figure 2 is a fragmentary transverse sectional view of the same taken on the plane indicated by the line 2 2 in Figure 1.

Figure 3 is a fragmentary view of the exterior of a rotor stage during assembly.

Figure 3a is a similar View after assembly.

Figure 4 is a sectional view taken on the plane indicated by the line 44 in Figure 3a.

Figure 4a is a sectional view taken on the plane indicated by the line 4a-4a in Figure 3.

Figure 5 is a fragmentary axonometric exploded view of the shroud.

Figure 6 is a fragmentary sectional view of a second embodiment of the invention taken in a plane containing the axis of the compressor.

Figure 7 is an external view of a portion of the shroud of Figure 6.

Figure 8 is a greatly enlarged detail of a portion of Figure 7.

Figure 9 is a fragmentary axonomet-ric exploded view of the shroud of Figures 6 to 8.

It may be noted that the drawings illustrate only the rotor structure of the compressor and only one stage, since the details of the stator structure are immaterial to the invention, and the structure of one stage may be duplicated for a number of stages of the compressor.

Referring to Figures 1 and 2, the rotor 10 may be of any suitable structure, but is illustrated as a composite rotor including a disk 11 and spacer rings 12 and 13 fixed ice to the disk by a ring of bolts 14. The spacer rings may be similarly fixed to similardisks to provide a multistage rotor which may include a central shaft or tiebolt 16. The rim 17 of the wheel is provided with slots to receive the dovetail roots 18 of compressor rotor blades 19. The blades may inelude platforms 21 adjacent the roots of the blades.

The blades extend radially outward from the disk and terminate at the blade tips 22. The blade tips are disposed in a ring. A blade shro ud or rotor shroud 24- made up of a number of arcuate segments 26 extends around the tips of the blades. The number of segments may be varied, but a suitable number of segments is six. The shroud segments are disposed end-to-end with the ends overlapping to provide the equivalent of a continuous shroud.

The shroud 24 of Figures 1 to 5 is of channel section with a web 27 and outwardly extending flanges 28. At one end of each shroud segment, a tongue 29 extends from the web 27 and is slightly offset radially so as to overlie the web 27 of the adjacent section. Rectangular openings 31 are punched in the web 27 and one such opening is punched in the tongue 29. These openings are disposed at such an angle to the axis of the compressor as to accord generally with the angle of the tip of the blade with respect to the compressor axis. The tip of each blade is machined to provide a neck 32 and a head 33, the neck and head together constituting a headed .tang 34 at; the end of the blade, The blade shroud is dropped over the headed tang 34 of each blade with the tang extending through the opening 31.

The shroud is retained on the blade by a locking clip 36 which may readily be attached and removed and which holds the shroud seated against the shoulders, 37' at the base of the tang. Figures 33, 3a, 4, and 4;; illustrate two stages in the mounting of the locking clip. The locking clip in Figures 3 and 4a has been dropped over the blade tang and the clip in Figures 3a and 4 has been rotated so as to engage between the head 33 of the tang and the shroud in a bayonet lock and has been locked against displacement. Each clip 36 is a formed sheet metal pant including a base 37 and an outwardly extending flange 38. An'opening 39 of irregular contour is cut in the base 37 of the clip. The greatest dimension of the opening is such that the clip may be dropped over the tang 34 of the blade. Portions 41 of the base of the clip at each end are deformed upwardly and are disposed so that upon rotation of the clip to the position shown in Figures 3a and 4, the portions 41 engage under the shoulders 3-3 of the tang, as illustrated in Figure 1. When the clip has been rotated into this position, it is locked against disengagement by bending down two tabs 42 extending upwardly from the base 37 so that the tabs will engage the neck 32 of the blade tang and prevent the clip from rotating into the position which frees the shroud. The deformed portions 41 will yield slightly and thus provide a slight tolerance in the fit. They are too stiff to yield under centrifugal force.

As will be apparent, the shroud is easily attached and removed. After the blades have been mounted in the disk, the segments of the shroud are put over the ends of the blades. The clips are put over the ends of the blades and rotated to fit under the tangs and are locked in place by bending down the tabs 42. If it is desired to remove blades for any reason, any or all segments of the shroud may easily be removed by bending up the tabs 42, rotating the clips, and lifting them off to free the shroud for removal.

The second form of shroud structure, illustrated in Figures 6 to 9, is similar in general to that previously described in that it involves a sheet metal shroud with overlapping segments fixed to the blades by locking clips. The differences are in the structure of the shroud, the provision of two tangs on each blade, and the use of a different locking clip. Considering first the structure of the shroud 51, this comprises a flat arcuate strip 52 and an outer strip 53 which may be described as being of W-shaped cross section. This strip has flanges at the edge like segments 26 shown in Figure 5, but also has a raised portion 54 at the center so that there are a total of four radial webs in the strip 53. The strips 53 abut the strips 52 and are brazed or spotwelded to them to provide a strong, stiff and lightweight shroud segment. Each blade 56 may be mounted in the same manner as shown for blades 19 in Figure 1, and the shroud 51 extends around the blades as does shroud 24 as shown in Figure 2. Each blade 56, however, has two tangs 57, each including a head 58 and a neck 59. The blade defines a shoulder 60 between the tangs and adjacent the leading and trailing edges against which the strip 52 bears. The strip 53 terminates short of one end of strip 52 and extends beyond the other end, as shown in Figure 9, so that the end portion 61 of strip 52 may underlie the end portion 62 of strip 53. Two rows of holes 63 and 64 are punched through the strips 52 and 53 to receive the tangs 57. At the joint between the shroud segments, the tangs go through the strip 52 of one shroud and the strip 53 of the other.

After the shrouds have been fitted over the tips of the blades, they are retained by locking clips 66, two for each blade. The clips 66 are cup-shaped, with a base 67 and a flange 63. An elongated opening 69 is punched in the base of the clip of such dimensions as to pass over the head 58 of the tang. Upon rotating the clip 90 degrees, the base of the clip engages under the head of the tang to provide a bayonet lock joint. Two small deformable tabs 71 brazed to the flange of the clip and standing upwardly from the flange before the clip is installed may then be bent down into the position shown in Figure 8 where they lie at each side of the head 58 and prevent the clip from rotating so as to release the shroud.

As will be seen, the advantages of this form of the invention are similar to those of the form previously described.

In both forms of the invention, a shroud which is light in Weight and yet rigid is provided. Because it is rigid, it will not be deformed significantly from its circular shape because of centrifugal force; because of its light weight, it will not put too heavy a centrifugal load on the blades. Both forms of shroud are beneficial in improving the air flow characteristics at the tip of the blade, in improving the seal between the blade tips and the compressor case, in greatly increasing the fundamental frequency of vibration of the blades, and in reducing the load on the blade root due to gas loads. The flanges at the edges of the shrouds may be ground to size and concentricity with the disk axis after the shrouds have been put on the blades to provide a close seal to the case.

The invention is not to be considered as restricted by the detailed description of the preferred embodiments thereof presented for the purpose of explaining the principles of the invention, as many modifications may be made by the exercise of skill in the art within the scope of the invention.

Certain structure illustrated but not claimed herein forms the subject matter of my divisional application for patent, Serial No. 9,995, filed February 19, 1960, entitled Attaching Devices.

I claim:

1. A shrouded turbomachine rotor structure comprising, in combination, a rotor, a ring of blades extending from the rotor, a shroud mounted on the tips of the blades, the shroud comprising a number of segments mounted end-to-end to provide a shroud around the tips of the blades, each shroud segment being of fabricated sheet metal comprising an arcuate strip of flat cross-section and an arcuate strip of W-shaped cross-section providing four radially extending webs stiffening the segments, the two strips being rigidly united to provide a composite arcuate shroud segment, and means for attaching the shroud to the blade comprising tangs with heads at the free ends of the blades, each blade providing an outwardly facing shoulder adjacent the tang head, the shroud abutting the shoulders and having openings for the tangs, the tangs extending through the openings, and clips lodged between the outer surface of the shroud and the heads of the tangs retaining the shrouds on the blades.

2. A rotor shroud comprising, in combination, a plurality of arcuate shroud segments disposed in overlapping end-to-end relation, each segment comprising an arcuate strip of flat cross-section and an arcuate strip of W- shaped cross-section providing four webs extending radially to the axis of the arc of the strip, the two strips being united to provide a composite arcuate shroud segment with one end of each strip extending beyond the end of the other strip, the shroud segments having openings therein to provide for attachment to blades of a rotor blade row. 

